1. Field of the Invention
The present invention relates to a substrate heating apparatus and manufacturing method for the same.
2. Description of the Related Art
As a substrate heating apparatus in a semiconductor manufacturing apparatus, ceramic heaters have been conventionally used. In this ceramic heater, a linear resistance heating element is buried in a disc-shaped ceramic base. A ceramic heater with an electrostatic chuck function has also been widely used. In this ceramic heater, an electrostatic chuck electrode used for fixing a substrate by suction, is buried in a ceramic base together with a resistance heating element.
In these ceramic heaters having resistance heating elements buried in ceramic bases, the bases are made of ceramics having high corrosion resistance and the resistance heating elements are not exposed to the outside environment. Therefore, such ceramic heaters are used suitably for a CVD (chemical vapor deposition) apparatus, a dry-etching apparatus or the like in which corrosive gas is often used.
Normally, these ceramic heaters have a disc shape. In a substrate heating apparatus used in a CVD apparatus or a dry-etching apparatus, the terminals of a resistance heating element are drawn out without being exposed to corrosive gas. In order to do so, a construction is often employed where a cylindrical member is joined to the center of bottom of the ceramic base, and the terminals of the resistance heating element as well as a power supply rod connected thereto are accommodated in the cylindrical member. (See Japanese Patent Laid-Open Publication No. 2003-133195).
In these conventional ceramic heaters, the evenness of the heating surface on which a substrate is placed has been ensured by lapping or the like in order to improve the adherence with the substrate and the efficiency of heat transfer. A substrate placed on a highly-even heating surface shows a temperature distribution reflecting that of the heating surface of the ceramic heater.
A ceramic heater used for a semiconductor manufacturing apparatus is used in a wide temperature range depending on use. However, in order to improve production yield, it is preferred that the temperature of a substrate be made as uniform as possible. Therefore, highly uniform temperatures are also required with regard to the temperature of the heating surface of a substrate heating apparatus on which a substrate placed.
However, in a generally disc-shaped ceramic heater without a cylindrical member, heat radiation from its peripheral part is high. Therefore, the temperature of the peripheral part tends to be lower than that of the center part of the heating surface.
On the other hand, in a ceramic heater with a cylindrical member joined to the backside of the ceramic base, the temperature of the central part of the heating surface tends to drop due to a major heat transfer from the cylindrical member. Once the temperature of the central part becomes lower than that of the peripheral part, the central part of the ceramic base shrinks and the peripheral part expands. As a result, tensile stress occurs at the central part of the ceramic base. Typically, the ceramic base is highly resistant to compression stress, but remains susceptible to tensile stress. Moreover, grooves for drawing out wiring or the like are concentrated in the central part of the ceramic base. Therefore, having a low temperature at the central part causes a problem with the strength of the ceramic heater. In order to enhance the strength of the ceramic heater having the cylindrical member, the temperature of the central part of the ceramic heater must be higher than that of the peripheral part so that compression stress occurs at the central part of the ceramic heater.
However, if the temperature of the central part of the heating surface is higher than that of the peripheral part, and the heat throughout the heating surface is not uniform in a ceramic heater with or without cylindrical member joined to the ceramic base, a substrate placed on the flat heating surface will show a temperature distribution which reflects that of the heating surface of the ceramic heater. This makes it difficult to achieve a uniform temperature distribution of the substrate.